"Arsenite...[incorporates into DNA] in the place of phosphate in the nucleotides during the synthesis of DNA."
You've seen this story all over the web in the last few days. Alien life! Life on other planets!! NASA is revived! Mars men get ready, 'cause here we come!But, in fact, is that really the story?
The report was published in Science Express this week and written about in the NYT -- and everywhere else you look:
Scientists said Thursday that they had trained a bacterium to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe or even here on Earth using biochemical powers we have not yet dared to dream about.
“There is basic mystery, when you look at life,” said Dimitar Sasselov, an astronomer at the Harvard-Smithsonian Center for Astrophysics and director of an institute on the origins of life there, who was not involved in the work. “Nature only uses a restrictive set of molecules and chemical reactions out of many thousands available. This is our first glimmer that maybe there are other options.”NASA, naturally enough, with its PR army always at the ready to instantly toot its own horn, didn't miss this juicy chance:
NASA-funded astrobiology research has changed the fundamental knowledge about what comprises all known life on Earth.So some bacteria were artificially selected to eat arsenic. What's the big deal here? Is this a big deal?
Caleb Scharf, an astrobiologist at Columbia University who was not part of the research, said he was amazed. “It’s like if you or I morphed into fully functioning cyborgs after being thrown into a room of electronic scrap with nothing to eat,” he said.Oh, that's it! It is a big deal! The bacteria morphed into cyborgs! Or rather, the arsenic insinuated itself into the bacterial DNA, by replacing phosphates in some of the nucleic acids. Is that a big deal?
That quote we started with?
It turns out that that quote with which we lead this post, in red, the one about arsenite incorporating into DNA, the big finding that NASA is touting, is from a paper published in 1980 -- 30 years ago -- about the health effects of arsenic and how and why it's so toxic. To humans. Give humans enough arsenic and they die, but we can survive lower levels. Kind of like bacteria. And that 1980 paper cites a 1974 paper, Petres, J., D. Baron and I. Kunick, Untersuchungen fiber arscnbedingte VerKndenmgen der Nueleinsauresynthase in vitro, Derm. Mschr., 160 (1974) 724--729 -- ok, it's in German, but it's still knowledge that's out there.)
Something largely new, worth knowing--important, even!
It's long been known that Arsenic is chemically similar to Phosphorous and can substitute in many biomolecueles, like protein and DNA, and their reactions. This is freshman chemistry. It has also been known that the arsenic alternatives are less stable than those involving phosphorous in these compounds and reactions.
What this new study showed was that these particular bacteria, chosen because they had already adapted to a high-aresenic environment, could be induced by artificial selection pressure to incorporate arsenic into their basic biomolecules. The study is a careful, sophisticated demonstration of this fact. The authors clearly state that the bacteria were already adapted--in the normal evolutionary way--to high-aresenic environment. What they then did was gradually feed a serially transferred culture of these bugs to increasing concentrations of arsenic and little or no added phosphorous. The bacteria that survived were able to substitute the arsenic for some, at least, of their biofunctions (including use to synthesize DNA).
This is worthy of publication in a major journal, and even newsworthy as showing the degree to which already adapted simple organisms can adapt further to a slowly changed environment. It shows the potential power of evolutionary adaptation, and the degree to which life could, in some ways, function in an arsenic, phosphorous-deprived environment.
But this is not a new life form, any more than a giraffe is a new life form. The idea that there is life that doesn't function exactly as we do is not new. After all, we have found anaerobic life, life in extremely hot, cold, salty etc. conditions on Earth. In most every way, these are ordinary bacteria and this is ordinary evolution followed by very carefully imposed artificial selection.
Were they happy?
And those little bacteria? They were much much happier when given phosphorus again after their arsenic bath. As the authors say, the bacterium "is not an obligate arsenophile and it grew considerably better when provided with P" [phosphorus] -- which means that it would not have survived natural selection in the presence of both chemicals.
Indeed, this study doesn't provide a scrap of evidence that such forms could evolve into stable complex life forms de novo without the help of strong, intentional, teleological and hence totally non-Darwinian evolution. Maybe it's possible, but this study shows nothing more than that bioreactions can occur, under some particular conditions, with the incorporation of arsenite in a complex cell already adapted to an arsenic environment. We aren't chemists so can't say how much this study furthers, if not really revolutionizes, ordinary biochemistry. The paper basically says nothing about life in NASA-land. That was almost entirely PR hyperbole--the usual self-promotion (not, we note, by the authors in their paper, though they were funded by NASA).
This paper can stand on its own legs as an interesting finding in biochemistry, or even a demonstration of the power of natural or artificial selection....but is there anything new here that wasn't already known in the 1974 German paper? Perhaps the latter (we don't read German well enough to judge) was an in vitro reaction rather than one occurring in a whole organism. If so, if this is a new finding about DNA synthesis in vivo, then responsible news media should just say that without all the ballyhooing and showmanship.
Do we know anything new about alien life?
As to alien life, what does this add? Let's now assume that the study shows that, in principle, life could exist without phosphorous and with arsenic. It has long been argued (wholly hypothetically, but let's not quibble about that either) that if there are billions of rocky planets in the universe (and, perhaps it's trillions, and perhaps there are many universes) and if even only a tiny fraction of those planets have classical earth-life conditions, then just statistically there must be thousands of planets with life that has at least some similarities with our own. That doesn't mean they use DNA with RNA intermediates, have brains or lipid cell membranes (or cells, for that matter). But even assuming that is statistically possible, it may exist on at least some planets somewhere out there. The larger space is, the more of these there statistically would be, on the basis just of probability. Of course such numbers games are fun, but prove nothing.
So what about the arsenic finding? Suppose, say, it doubled the fraction of planets that would have this additional life-possible make-up. By playing the same numbers game, this would just raise the hypothetical number of planets with life on them by, say, a factor of two. It doesn't change a single thing we've thought or known before. Even if we assumed that the new result showed that arsenic could work.
It also doesn't raise by any serious amount the likelihood we'll find such planets, that we'll talk to the little green arseno-Men who live on them, or anything else.
Are we condemned to live in a world in which everything has to be boasted about, or turned into entertainment? Is it OK for science to be turned into fun in this way? Or is it irresponsible?
Science is interesting in its own right, and we know that, left alone, it will lead, if unpredictably, to increased and interesting knowledge, and improved standards of living. But the hype-route obviously isn't working to make a population that's more deeply understanding of science. It makes a population that (in the US) largely doesn't even 'believe' in evolution, and perhaps increasingly can't tell fact from fiction.
